Yesterday I talked about using System.Xml in the new object model. My code examples included a key part of the InfoPath programming model: looking up fields in the data source using XPath so that you can set and get values.
Unfortunately, figuring out the absolute XPath to a field can be a pain.
Fortunately, we've made that easy in InfoPath 2007.
Right click the field in the Data Source task pane and click Copy XPath
Now you can paste the XPath into your code and be on your merry way.
Hope that helps,